Which mechanism in a circuit breaker trips when protecting an overloaded circuit?

• A. The fuse element melts
• B. The magnetic trip coil activates
• C. The arc chute opens the contacts
• D. The bi metallic strip distorts and trips

Answer: (C)

When a circuit breaker protects against an overloaded circuit, the overcurrent causes heating, and the mechanism that reacts is a bi-metallic strip inside the device. This strip is made of two metals with different expansion rates; as it heats, one metal expands more than the other, bending the strip. The bending releases the trip latch and opens the contacts, stopping the current flow. The arc chute’s job is to help manage the arc after the contacts separate, not to trigger the trip. The magnetic trip coil, if present, is used for fast trips during short circuits, not for normal overload protection, and a fuse element melting belongs to fuses, not circuit breakers.